Field of the Invention
The present invention relates to a method of generating a channel quality indicator in a mobile communication system, and specifically, considering a downlink channel status to adaptively adjust the number of frequency bands for channel quality indicator measurement and a width of a frequency band for the channel quality indicator measurement in a frequency-selective channel of a mobile communication system.
Discussion of the Related Art
Generally, channel information is fed back for efficient communication. For example, downlink channel information is uploaded and uplink channel information is downloaded. This channel information is referred to as a channel quality indicator (CQI). The CQI may be generated by a variety of methods. For example, the CQI may be reported by quantizing and uploading a channel status, by calculating and uploading SINR (Signal to Interference plus Noise Ratio), or by announcing a real channel status such as MCS (modulation coding scheme) level.
The CQI is most often generated according to the MCS level. The CQI should change according to the change in the modulation scheme and the coding scheme. Therefore, at least one CQI is necessary per codeword unit.
The number of CQIs increases if a MIMO (Multiple-input Multiple-output) is applied to a system. Specifically, several codewords may be simultaneously transmitted since MIMO systems generate multi-channels using multi-antennas. Thus, several CQIs should be reported correspondingly. As such, the size of control information is proportionally increased if a plurality of CQIs are used.
FIG. 1 illustrates a diagram for generation and transmission of CQI.
As illustrated in FIG. 1, a user equipment 100 measures a downlink quality and then reports a CQI value to a base station 200 via uplink control channel. The CQI value is selected according to the measured downlink quality.
The base station 200 may perform downlink scheduling, user equipment selection, and resource allocation, according to the reported CQI. The CQI value may include one of SINR (signal to interference and noise ratio) of a channel, CINR (carrier to interference and noise ratio), BER (bit error rate), FER (frame error rate), or a value resulting from converting one of the values above to transmittable data. In a MIMO system, information reflecting a channel status such as RI (rank information), PMI (precoding matrix information), may be added to the CQI value.
In a mobile communication system, link adaptation is used to maximize the use channel capacity of a channel. The link adaptation provides a method of adjusting MCS (modulation and coding set) and transmission power according to a given channel. The channel quality information must be fed back to a base station to enable the base station to perform the link adaptation.
Abrupt channel variation appears within a system bandwidth if a frequency band used by a system exceeds a coherence bandwidth. Specifically, in a multi-carrier system such as an orthogonal frequency division multiplexing (OFDM) system, several subcarriers exist within a given bandwidth. Since modulated symbols are transmitted via each of the subcarriers, optimal channel transmission means that channel information is carried by each subcarrier. Therefore, the size of the channel information is abruptly raised in a multi-carrier system having a plurality of subcarriers.